Kittens and cats living in groups have an assortment of infectious diseases to contend with: upper respiratory infections, coronavirus, coccidia, to name a few. Tritrichomonas foetus is yet another infectious organism yielding diarrhea in feline patients, usually with a history of group lifestyle. This organism was previously thought to infect only cattle where it causes miscarriage and fertility problems, but recently (in 2003) T. foetus has emerged as an infectious agent for cats. Information and recommendations regarding this organism have changed in the last several years and we attempt to provide the most up to date summary of what is known and recommended for prevention and treatment of this infection.

WHAT IS TRITRICHOMONAS FOETUS ANYWAY?

The short answer is that this is a single-celled organism. The longer version is that this is a flagellate, a single-celled organism possessing lash-like structures, called “flagella,” on its “body” which wave around allowing the organism to move. T. foetus is commonly mistaken for Giardia, another parasitic flagellate as they both use flagella to move around and both have pear shaped bodies.

Giardia organism

Tritrichomonas foetus

HOW DO CATS GET INFECTED?

T. foetus organisms are shed in the feces of an infected cat. Most commonly, transmission occurs when cats share a litter box as the organism can live up to 3 days in fecal material. Any time a cat steps in the feces of an infected cat, organisms can be transferred to the paws and later licked up during grooming.

WHAT DOES IT DO TO THE CAT?

T. foetus colonizes the lower intestine of the cat causing the mucous and sometimes bloody diarrhea that characterizes colitis. If the colon is biopsied, inflammatory cell infiltration typical of inflammatory bowel disease will be seen. Infected cats do not always have diarrhea; many cats especially older ones have no symptoms at all but are still contagious to other cats.

Because colitis can have so many causes, it is important to keep this possible cause in mind. Chronic colitis may or may not respond to symptomatic treatment and if a specific underlying cause can be identified and treated, a long-term difficult problem can be potentially resolved permanently. Many colitis remedies will lead to temporary improvement for a Tritrichomonas-infected cat but the symptoms generally come right back after treatment ceases.

MAKING THE DIAGNOSIS

There are presently four testing methods that can be used to identify Tritrichomonas foetus in a fecal sample. It should be noted that a proper fecal sample for testing must be freshly voided (i.e. immediately retrieved from the anus with no cat litter contamination), obtained with a deeply inserted fecal loop, or flushed from the colon with a syringe. Bringing a sample from home will not be adequate. If the cat has been on antibiotics, this will interfere with testing; the cat should be off antibiotics for at least a couple of days.

Direct SmearHere some fecal matter is swabbed onto a microscope slide, mixed with a gentle saline solution, and examined for the presence of flagellate organisms. The feces must be immediately fresh from the rectum. The wetter and more mucous the sample, the better. Usually several slides must be examined as the organism is elusive. Standard fecal tests for parasites will not pick up this organism. Refrigeration of the sample will kill the organism and make it impossible to detect. Further, if the patient is on antibiotics the number of organisms available to detect will be greatly reduced even though most antibiotics cannot cure the infection.

While this is a relatively easy test to perform, it only has about a 14% chance of detecting a natural T. foetus infection. A more sensitive test is generally preferred.

Culture (also called the “Pouch Test”)

A special culture bag can be used to grow T. foetus in numbers large enough for detection. The feces used must be freshly obtained from the rectum, inoculated into the pouch, and the pouch is kept in a vertical position for 12 days at room temperature. The pouch is periodically examined under the microscope for the presence of organisms.

This is the test method of choice in most cases as it is easy to perform, reasonably priced and generally accurate.

PCR Testing (Polymerase Chain Reaction Testing)

PCR testing is a DNA test for the presence of T. foetus. A larger fecal sample is needed and the test must be done at a reference lab. It is generally reserved for patients where the Pouch test has been negative but the index of suspicion is still high.

PCR testing is the most sensitive of all the test methods but is also fairly expensive. Specialized equipment is needed and only a few laboratories are qualified to run samples.

Biopsy

A routine colon biopsy is unlikely to find this parasite; special stains on the tissue (“immunohistochemistry”) must be requested and at least six tissue samples must be examined. This is the most invasive form of testing and would not be done right off the bat but if the patient is going to have a biopsy for chronic colitis anyway, it might be a good idea to have the pathologist look for T. foetus.

A negative test never rules out Tritrichomonas infectionno matter which test is performed.

TREATMENT

In the past several different antibiotics have been reported to be effective but it turns out that this is probably an overestimate since 88% of cats will resolve their diarrhea spontaneously within 2 years. They will still be infected, or at least 57% of them will, but will have normal stool and they may relapse with stress.

One treatment option is to simply wait for resolution if the household does not have a large number of cats and the diarrhea is not excessive.

The only drug that is felt to be reliable against T. foetus is ronidazole, and its use is far from straight-forward. Here is what to know:

Ronidazole must be compounded to get a dose in a suitable size for cats.

Ronidazole is not licensed for use in cats; it is a poultry antibiotic. It also tastes very bad and should be provided in capsules rather than as an oral liquid so as to avoid the taste.

The owner must wear gloves when handling ronidazole.

The most common side effect in cats is neurotoxicity which means it is not appropriate to use ronidazole as a trial to see if a cat with colitis improves on it. Ronidazole should be used only in confirmed Tritrichomonas patients.

Neurotoxicity manifests as loss of appetite, incoordination, and possibly seizures. Some experts recommend engaging the cat in play on a daily basis to assess muscular coordination and agility.

Cats being treated should be isolated from other cats in the home to prevent reinfection.

It is not possible to fully confirm that an infection has been eradicated as a negative PCR test does not rule out infection. Experts recommend a PCR test in 1-2 weeks after treatment and again 20 weeks after treatment as the closest we can come to confirming eradication.

Ronidazole is usually given once daily for two weeks. The diarrhea should be resolved by the end of this course